Light emitting diode having carbon nanotubes

ABSTRACT

A light emitting diode includes a substrate, a first semiconductor layer, an active layer, a second semiconductor layer, a first electrode, a second electrode, a static electrode and a carbon nanotube structure. The first semiconductor layer, the active layer, and the second semiconductor layer are stacked on the substrate. The first electrode is located on and electrically connected to the first semiconductor layer. The carbon nanotube structure is located on and electrically connected to the second semiconductor layer. The second electrode is located on and electrically connected to the carbon nanotube structure. The static electrode is located between the second semiconductor layer and the carbon nanotube structure. The carbon nanotube structure includes a first portion in direct contact with the second semiconductor layer and a second portion sandwiched between the static electrode and the second electrode.

RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 14/678,186, filed on Apr. 3, 2015, entitled “LIGHTEMITTING DIODE HAVING CARBON NANOTUBES,” which is a continuationapplication of U.S. patent application Ser. No. 12/584,417, filed onSep. 3, 2009, entitled “LIGHT EMITTING DIODE HAVING CARBON NANOTUBES,”which claims all benefits accruing under 35 U.S.C. § 119 from ChinaPatent Applications: Application No. 200810217913.3, filed on Nov. 28,2008 in the China Intellectual Property Office, disclosures of which areincorporated herein by references.

BACKGROUND 1. Technical Field

The present disclosure relates to a light emitting diode (LED).

2. Description of the Related Art

LEDs are semiconductors that convert electrical energy into light.Compared to conventional light sources, the LEDs have higher energyconversion efficiency, higher radiance (i.e., they emit a largerquantity of light per unit area), longer lifetime, higher responsespeed, and better reliability. At the same time, LEDs generate lessheat. Therefore, LED modules are widely used in particular as asemiconductor light source in conjunction with imaging optical systems,such as displays, projectors, and so on.

Referring to FIG. 6, a typical LED 10, according to the prior artincludes a substrate 110, a GaN bumper layer 120, an N-type GaN layer132, an active layer 134, a P-type GaN layer 136, and a transparentcontact layer 140. The GaN bumper layer 120, the N-type GaN layer 132,the active layer 134, the P-type GaN layer 136, and the transparentcontact layer 140 are stacked on the substrate 110. The LED 10 furtherincludes a transparent conductive layer 150, a first electrode 142, anda second electrode 144. The first electrode 142 is disposed on theN-type semiconductor layer 132. The transparent conductive layer 150 andthe second electrode 144 are disposed on the transparent contact layer140. The transparent conductive layer 150 is made of indium tin oxide(ITO) and the ITO is sputtered on an area of the transparent contactlayer 140. Due to the net structure of the ITO layer, the lateraldistribution of current applied on the transparent conductive layer 150is uniform, thereby improving the extraction efficiency of light of theLED. However, the ITO layer has some faults, such as low mechanicalstrength and resistance distribution. Furthermore, the transparency ofthe ITO layer may be decreased in humid environments and the ITO layermay absorb some of the light emitted by the active layer 134 when theITO fully covers the P-type semiconductor layer 136.

What is needed, therefore, is a light emitting diode, which can overcomethe above-described shortcomings.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the embodiments can be better understood with referenceto the following drawings. The components in the drawings are notnecessarily drawn to scale, the emphasis instead being placed uponclearly illustrating the principles of the embodiments. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 is a schematic, partial exploded view of a light emitting diodeaccording to an embodiment.

FIG. 2 is a schematic view of the light emitting diode of FIG. 1.

FIG. 3 is a scanning electron microscope (SEM) image of a carbonnanotube film used in the light emitting diode of FIG. 1.

FIG. 4 is a schematic view of a light emitting diode according to ananother embodiment.

FIG. 5 is a schematic view of a light emitting diode according to anembodiment.

FIG. 6 is schematic, cross-sectional view of a typical light emittingdiode according to prior art.

FIG. 7 is a schematic structural view of a carbon nanotube segment ofthe drawn carbon nanotube film.

FIG. 8 is a SEM image of two cross-stacked drawn carbon nanotube films.

FIG. 9 is a schematic view of two cross-stacked drawn carbon nanotubefilms.

DETAILED DESCRIPTION

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “an” or “one” embodiment in this disclosure are not necessarily tothe same embodiment, and such references mean at least one.

Referring to FIG. 1 and FIG. 2, a first embodiment of a light emittingdiode (LED) 20 includes a substrate 210, a first semiconductor layer232, an active layer 234, a second semiconductor layer 236, a firstelectrode 242, a second electrode 244, a transparent conductive layer250, and a static electrode 240. The first semiconductor layer 232, theactive layer 234, the second semiconductor layer 236 are orderly stackedon the substrate 210. The first electrode 242 is electrically connectedto the first semiconductor layer 232. The transparent conductive layer250 is disposed on the top surface of the second semiconductor layer 236and electrically connected to the second semiconductor layer 236. Thestatic electrode 240 is interposed between the second semiconductorlayer 236 and the transparent conductive layer 250. The second electrode244 is disposed on the top surface of the transparent conductive layer250 and electrically connected to the transparent conductive layer 250.

The substrate 210 may have a thickness of about 300 microns (μm) toabout 500 μm and a transparent plate for supporting the other elements,such as the first and second semiconductor layers 232, 236. Thesubstrate 210 may be made of sapphire, gallium arsenide, indiumphosphate, silicon nitride, gallium nitride, zinc oxide, aluminumsilicon nitride, silicon carbon, or their combinations. In oneembodiment, the substrate 210 is made of sapphire and has a thickness of400 μm.

The first semiconductor layer 232, the active layer 234, and the secondsemiconductor layer 236 can be stacked on the substrate 210 via aprocess of metal organic chemical vapor deposition (MOCVD).

The first semiconductor layer 232 has a thickness of about 1 μm to about5 μm. The second semiconductor layer 236 has a thickness of about 0.1 μmto about 3 μm. When the first semiconductor layer 232 is an N-typesemiconductor, the second semiconductor layer 236 is a P-typesemiconductor, and vice versa. In one embodiment, the firstsemiconductor layer 232 is an N-type semiconductor and the secondsemiconductor layer 236 is a P-type semiconductor. The firstsemiconductor layer 232 has a step-shaped structure and includes a firstsurface 262 and a second surface 264 located on the same side as thefirst surface 262. The first surface 262 and the second surface 264 havedifferent heights and form a step-shaped structure. The active layer 234and the second semiconductor layer 236 are arranged on the first surface262.

The first semiconductor layer 232 is configured to provide electrons,and the second semiconductor layer 236 is configured to providecavities. When a voltage is applied to the first and secondsemiconductor layers 232, 236, the electrons can flow into the secondsemiconductor 236 and incorporate with the cavities, thereby emittinglight. The first semiconductor layer 232 may be made of N-type galliumnitride, N-type gallium arsenide, or N-type copper phosphate. The secondsemiconductor layer 236 may be made of P-type gallium nitride, P-typegallium arsenide, or P-type copper phosphate. In one embodiment, thefirst semiconductor layer 232 is made of N-type gallium nitride and hasa thickness of 2 μm, and the second semiconductor layer 236 is made ofP-type gallium nitride and has a thickness of 0.3 μm.

The active layer 234, in which the electrons fill the holes, has athickness of about 0.01 μm to about 0.6 μm. The active layer 234 is aphoton exciting layer and can be one of a single quantum well layer ormultilayer quantum well films. The active layer 140 can be made ofGaInN, AlGaInN, GaSn, AlGaSn, GaInP, or GalnSn. In one embodiment, theactive layer 234 has a thickness of 0.3 μm and includes one layer ofGaInN stacked with a layer of GaN.

The static electrode 240 is formed on the top surface of the secondsemiconductor layer 236. The static electrode 240 may be a P-typeelectrode or an N-type electrode and is a same type as the secondsemiconductor layer 236. Therefore, in one embodiment, the staticelectrode 240 is a P-type electrode. Understandably, the staticelectrode 240 can function as a reflection layer. The static electrode240 can have one or more layers of metal and may be made of titanium,aluminum, nickel, gold, or any combinations thereof. In one embodiment,the static electrode 240 has two layers. One layer is made of titaniumand has a thickness of 15 nanometers (nm). The other layer is made ofgold and has a thickness of 100 nm. The static electrode 240 is formedon the second semiconductor layer 236 via a process of physical vapordeposition, such as electron evaporation, vacuum evaporation, ionsputtering, or the like.

Further, a functioning layer may be formed between the substrate 210 andthe first semiconductor layer 232. The functioning layer may be one ormore of a buffer layers, a reflective layer, and a photon crystalstructure. The buffer layer is configured to improve epitaxial growthand decrease lattice mismatch. The buffer layer may be made of GaN, AlN,or the like. The reflective layer is configured to change thetransmission route of the light to improve extraction efficiency oflight in the LED. The reflective layer may be made of silver, aluminum,rhodium, or the like. The photon crystal structure is configured toimprove extraction efficiency of light and may be made of silicon,indium tin oxide, carbon nanotube, or the like. In one embodiment, onlythe buffer layer 220 is formed on the substrate 210 and is made of GaN.The buffer layer 220 has a thickness of about 20 nm to about 50 nm.

The transparent conductive layer 250 includes a carbon nanotubestructure. The transparent conductive layer 250 can be directly appliedto the top surface of the second semiconductor layer 236 and the staticelectrode 240. The transparent conductive layer 250 may only cover theexposed surface of the second semiconductor layer 236 and fully orpartly cover both the top surface of the static electrode 240 and thesecond semiconductor layer 236. In one embodiment, the transparentconductive layer 250 fully covers both the second semiconductor layer236 and the static electrode 240. The carbon nanotube structure mayinclude at least one carbon nanotube film and/or a number of carbonnanotube wires. The use of all types of carbon nanotube films and/orcarbon nanotube wires is envisioned to be employed by the transparentconductive layer 250. There is no particular restriction on thethickness of the carbon nanotube structure and it may be appropriatelyselected depending on the purpose, and may be, for example, greater than0.5 nm, and more specifically from about 0.5 μm to 200 μm.

The carbon nanotube structure can include one or more layers of carbonnanotube films. When the carbon nanotube structure includes a number ofcarbon nanotube films, the carbon nanotube films are stacked on top ofeach other. The carbon nanotube structure can employ more carbonnanotube films to increase the tensile strength of the carbon nanotubecomposite. The carbon nanotube film has a thickness in an approximaterange from about 0.5 nm to about 100 mm. The carbon nanotubes films mayhave a free-standing structure. The film structure being supported byitself and does not require a substrate to maintain its structuralintegrity. As an example, a corner of the carbon nanotube film can belifted without resulting in damage to the entire structure.

Referring to FIG. 3, the carbon nanotube films each is formed by thecarbon nanotubes, orderly or disorderly, and has substantially a uniformthickness. Ordered carbon nanotube films include films where the carbonnanotubes are arranged along a primary direction. Examples include filmswherein the carbon nanotubes are arranged approximately along a samedirection or have two or more sections within each of which the carbonnanotubes are arranged approximately along a same direction (differentsections can have different directions). In the ordered carbon nanotubefilms, the carbon nanotubes are oriented along the same preferredorientation and approximately parallel to each other. A film can bedrawn from a carbon nanotube array, to form the ordered carbon nanotubefilm, namely a drawn carbon nanotube film. Examples of drawn carbonnanotube film are taught by U.S. Pat. No. 7,045,108 to Jiang et al., andWO 2007015710 to Zhang et al. Referring to FIG. 7, the drawn carbonnanotube film 143 includes a plurality of successive and oriented carbonnanotubes 145 joined end-to-end by van der Waals attractive forcetherebetween. The drawn carbon nanotube film 143 is a free-standingfilm. The carbon nanotube film 143 can be treated with an organicsolvent to increase the mechanical strength and toughness of the carbonnanotube film 143 and reduce the coefficient of friction of the carbonnanotube film 143. A thickness of the carbon nanotube film 143 can rangefrom about 0.5 nanometers to about 100 micrometers.

The ordered carbon nanotube film may be a pressed carbon nanotube filmhaving a number of carbon nanotubes arranged along a same direction. Thecarbon nanotubes in the pressed carbon nanotube film can rest upon eachother. Adjacent carbon nanotubes are attracted to each other andcombined by van der Waals attractive force. An angle between a primaryalignment direction of the carbon nanotubes and a surface of the pressedcarbon nanotube film is 0 degree to approximately 15 degrees. Thegreater the pressure applied, the smaller the angle formed. Thethickness of the pressed carbon nanotube film ranges from about 0.5 nmto about 1 mm. Examples of pressed carbon nanotube film are taught by USapplication 20080299031A1 to Liu et al.

The disordered carbon nanotube film comprises carbon nanotubes arrangedin a disorderly fashion. Disordered carbon nanotube films includerandomly aligned carbon nanotubes. When the disordered carbon nanotubefilm comprises of a film wherein the number of the carbon nanotubesaligned in every direction is substantially equal, the disordered carbonnanotube film can be isotropic. The disordered carbon nanotubes can beentangled with each other and/or are substantially parallel to a surfaceof the disordered carbon nanotube film. The disordered carbon nanotubefilm may be a flocculated carbon nanotube film. The flocculated carbonnanotube film can include a plurality of long, curved, disordered carbonnanotubes entangled with each other. The carbon nanotubes can besubstantially uniformly dispersed in the flocculated carbon nanotubefilm. Adjacent carbon nanotubes are attracted by van der Waalsattractive force to form an entangled structure with micropores definedtherein. It is understood that the flocculated carbon nanotube film isvery porous. Sizes of the micropores can be less than 10 μm. Due to thecarbon nanotubes in the flocculated carbon nanotube film being entangledwith each other, the carbon nanotube structure employing the flocculatedcarbon nanotube film has excellent durability, and can be fashioned intodesired shapes with a low risk to the integrity of the flocculatedcarbon nanotube film. The thickness of the flocculated carbon nanotubefilm can range from about 0.5 nm to about 1 millimeter (mm).

The disordered carbon nanotube film may be a pressed carbon nanotubefilm having a number of carbon nanotubes arranged along differentdirections. The pressed carbon nanotube film can be a free-standingcarbon nanotube film. When the carbon nanotubes in the pressed carbonnanotube film are arranged along different directions, the pressedcarbon nanotube film can be isotropic. As described above, the thicknessof the pressed carbon nanotube film ranges from about 0.5 nm to about 1mm. Examples of pressed carbon nanotube film are taught by USapplication 20080299031A1 to Liu et al.

Length and width of the carbon nanotube film can be arbitrarily set asdesired. A thickness of the carbon nanotube film is in a range fromabout 0.5 nm to about 100 μm. The carbon nanotubes in the carbonnanotube film can be single-walled, double-walled, multi-walled carbonnanotubes, and combinations thereof. Diameters of the single-walledcarbon nanotubes, the double-walled carbon nanotubes, and themulti-walled carbon nanotubes can, respectively, be in the approximaterange from about 0.5 nm to about 50 nm, about 1 nm to about 50 nm, andabout 1.5 nm to about 50 nm.

The carbon nanotube structure include a number of carbon nanotube wires.The carbon nanotube wires may be arranged side by side on the topsurface of the second semiconductor layer or may be weaved into a carbonnanotube layer. The weaved carbon nanotube layer is applied to thesecond semiconductor layer. The carbon nanotube wire includes untwistedcarbon nanotube wire and twisted carbon nanotube wire. The untwistedcarbon nanotube wire includes a number of carbon nanotubes parallel toeach other. The twisted carbon nanotube wire includes a number of carbonnanotube helically twisted along a longitudinal axis of the twist carbonnanotube wire. In other embodiments, the carbon nanotube structureincludes a drawn carbon nanotube film, the drawn carbon nanotube filmincludes a plurality of carbon nanotubes, the carbon nanotubes aresubstantially parallel to each other. The carbon nanotube structureincludes at least one carbon nanotube film, the carbon nanotube filmincludes a plurality of carbon nanotubes joined by van der Waals force.In one embodiment, the carbon nanotube structure includes two drawncarbon nanotube films, and an angle between aligned directions of thedrawn carbon nanotube films is approximately 90 degrees. The drawncarbon nanotube film includes a plurality of carbon nanotube segmentsjoined end to end by van der Waals force along an axial direction of thecarbon nanotubes.

The untwisted carbon nanotube wire can be formed by treating the drawncarbon nanotube film with an organic solvent. The drawn carbon nanotubefilm is treated by applying the organic solvent to the carbon nanotubefilm while being free to bundle. After being soaked by the organicsolvent, the adjacent paralleled carbon nanotubes in the drawn carbonnanotube film will bundle together, due to the surface tension of theorganic solvent when the organic solvent volatilizing, and thus, thedrawn carbon nanotube film will be shrunk into untwisted carbon nanotubewire. The carbon nanotubes of the untwisted carbon nanotube wires aresubstantially parallel to each other along the longitudinal axis of theuntwisted carbon nanotube wires. Examples of the untwisted carbonnanotube wire are taught by U.S. Pat. No. 7,045,108 to Fan et al. and USpublication No. 20070166223 to Fan et al.

The twisted carbon nanotube wire can be formed by twisting a drawncarbon nanotube film by using a mechanical force to turn the two ends ofthe drawn carbon nanotube film in opposite directions. Further, thetwisted carbon nanotube wire can be treated by applying the organicsolvent. After applying the organic solvent, the adjacent carbonnanotubes in the twisted carbon nanotube film will bundle together, dueto the surface tension of the organic solvent when the organic solventvolatilizing, and thus, the twisted carbon nanotube wire may have lessspecific surface area, and larger density and strength than an untreatedtwisted carbon nanotube wire.

The transparent conductive layer 250 may be made by steps of forming ametal layer (not shown) on the carbon nanotube structure and heating themetal layer in a temperature of about 300 degrees centigrade to about500 degrees centigrade for about 3 minutes to about 10 minutes. Themetal layer may be a single-layer structure or a multi-layeredstructure. In one embodiment, the metal layer includes a nickel layerstacked with a gold layer. The nickel layer has a thickness of about 2nm. The gold layer has a thickness of 5 nm. Since the metal layerdecreases in thickness because of the heating, the metal molecule of themetal layer can be melted and can aggregate into a number of metalparticles by surface tension. The carbon nanotube structure has aplurality of micropores between adjacent carbon nanotubes of the carbonnanotube structure. These metal particles uniformly disperse in themicropores of the carbon nanotube structure to form a composite film.The composite film, which functions as the transparent conductive layer250, has better electrical conductivity than the pure carbon nanotubestructure, thereby improving current injection efficiency and electricalcontact between the carbon nanotube structure and the static electrode240, the first electrode 242, and the second semiconductor layer 236.

In one embodiment, two drawn carbon nanotube films are coated on thesecond semiconductor layer 236 and the static electrode 240. An anglebetween the primary directions of the two drawn carbon nanotube filmsranges from about 0 degrees to about 90 degrees. In one embodiment, theprimary directions of the two drawn carbon nanotube films areperpendicular to each other as shown in FIGS. 8 and 9.

The second electrode 244 can be deposited on the transparent conductivelayer 250 via physical vapor deposition and may have single-layerstructure or multi-layered structure. The second electrode 244 can bemade of titanium or gold. In one embodiment, the second electrode 244includes two layers, one layer is titanium and has a thickness of 15 nmand another layer is gold and has a thickness of 200 nm. At least aportion of the carbon nanotube structure is located between the staticelectrode 240 and the second electrode 244. The second electrode 244 maybe P-type or N-type electrode and is the same type as the staticelectrode 240 and the second semiconductor layer 236. Since the staticelectrode 240 is made of P-type material, the second electrode 244 is aP-type electrode. When the LED 20 has the static electrode 240, thesecond electrode 244 should be located above the static electrode 240.When the LED has no static electrode 240, the second electrode 244 canbe located at any position on the transparent conductive layer 250. Inone embodiment, since the LED employs the static electrode 240, thesecond electrode 244 is located above the static electrode 240. Thesecond electrode 244 and the static electrode 240 function together asthe P-type electrode of the LED.

The second electrode 244 is a same polarity type with the firstsemiconductor layer 236 and may be made of N-type material. The secondelectrode 244 is deposited on the second surface 264 of the firstsemiconductor layer 236. The second electrode 244 has a same structureas the first electrode 242 and includes a titanium layer and a goldlayer stacked on the titanium layer. The titanium layer has a thicknessof about 15 nm and the gold layer has a thickness of about 200 nm. Themethod of depositing the second electrode 244 can be the same as that ofthe first electrode 242. The first and second electrodes 242, 244 can bedeposited at the same time.

Referring to FIG. 4, in one embodiment, an LED 30 includes a substrate310, a buffer layer 320, a first semiconductor layer 332, an activelayer 334, a second semiconductor layer 336, a first electrode 342, asecond electrode 344, a transparent conductive layer 350, and a staticelectrode 340. The buffer layer 320, the first semiconductor layer 332,the active layer 334, the second semiconductor layer 336 are orderlystacked on the substrate 310.

The first semiconductor layer 332 includes a first surface 362 and asecond surface 364 located on the same side as the first surface 362.The first surface 362 and the second surface 364 have different heightsand form a stepped structure. The active layer 334 and the secondsemiconductor layer 336 are disposed on the first surface 362. Thetransparent conductive layer 350 is disposed on the second surface 364of the first semiconductor layer 332 and electrically connected to thefirst semiconductor layer 332. Further, the static electrode 340 isinterposed between the first semiconductor layer 332 and the transparentconductive layer 350. The first electrode 342 is disposed on the topsurface of the transparent conductive layer 350 and electricallyconnected to the transparent conductive layer 350. The second electrode344 is electrically connected to the second semiconductor layer 336.

Referring to FIG. 5, in one embodiment, an LED 40 includes a substrate410, a buffer layer 420, a first semiconductor layer 432, an activelayer 434, a second semiconductor layer 436, a first electrode 442, asecond electrode 444, a first transparent conductive layers 450, asecond transparent conductive layer 452, and a first static electrode440, a second static electrode 446. The buffer layer 420, the firstsemiconductor layer 432, the active layer 434, the second semiconductorlayer 436 are orderly stacked on the substrate 310.

The first semiconductor layer 432 includes a first surface 462 and asecond surface 464 located on the same side a the first surface 462. Thefirst surface 462 and the second surface 464 have different heights andform a stepped structure. The second transparent conductive layer 452 ismounted on the second semiconductor layer 436, and the first transparentconductive layer 450 is mounted on the second surface 464 of the firstsemiconductor layer 432. Further, the first static electrode 440 islocated between the second semiconductor layer 436 and the secondtransparent conductive layer 452, and the second electrode 444 isdisposed on the top surface of the second transparent conductive layer452. The second static electrode 446 is interposed between the firstsemiconductor layer 436 and the first transparent conductive layer 450,and the first electrode 442 is disposed on the top surface of the firsttransparent conductive layer 450.

Since the carbon nanotubes have better electrical conductivity andmechanical strength than conventional material, such as indium tinoxide, the carbon nanotube structure has better electrical conductivityand mechanical strength, thereby improving power efficiency and lifespan. Further, the carbon nanotube structure is transparent in variedhumid environments. Therefore less of the light emitted by the activelayer is absorbed. Thus, the LED has good extraction efficiency incomparison with the typical LED.

It is to be understood, however, that even though numerouscharacteristics and advantages of the present embodiments have been setforth in the foregoing description, together with details of thestructures and functions of the embodiments, the disclosure isillustrative only, and changes may be made in detail, especially inmatters of shape, size, and arrangement of parts within the principlesof the disclosure to the full extent indicated by the broad generalmeaning of the terms in which the appended claims are expressed.

What is claimed is:
 1. A light emitting diode comprising: a substrate; afirst semiconductor layer located on the substrate, wherein the firstsemiconductor layer is a stepped structure comprising a first surfaceand a second surface lower than the first surface; an active layerlocated on the first surface of the first semiconductor layer; a secondsemiconductor layer located on the active layer; a first electrodelocated on the second surface of the first semiconductor layer andelectrically connected to the first semiconductor layer; a transparentconductive layer located on and electrically connected to the secondsemiconductor layer, wherein the transparent conductive layer comprisesa carbon nanotube structure; a second electrode located on andelectrically connected to the transparent conductive layer; and a staticelectrode located between the second semiconductor layer and the carbonnanotube structure, wherein the carbon nanotube structure comprises afirst portion in direct contact with the second semiconductor layer anda second portion sandwiched between the static electrode and the secondelectrode, and the static electrode is a continuous metal layer; whereinthe static electrode and the second electrode have a same shape and areaand completely overlap with each other.
 2. The light emitting diode ofclaim 1, wherein the carbon nanotube structure is a free-standingstructure.
 3. The light emitting diode of claim 1, wherein the carbonnanotube structure comprises a carbon nanotube film.
 4. The lightemitting diode of claim 3, wherein the carbon nanotube film comprises aplurality of carbon nanotubes joined end-to-end by van der Waalsattractive force therebetween and substantially parallel to each other.5. The light emitting diode of claim 4, wherein the carbon nanotubestructure comprises two carbon nanotube films stacked with each other,and an angle between aligned directions of carbon nanotubes of the twocarbon nanotube films is about 90 degrees.
 6. The light emitting diodeof claim 3, wherein the carbon nanotube film comprises a plurality ofcarbon nanotubes entangled with one another.
 7. The light emitting diodeof claim 1, wherein the carbon nanotube structure comprises a pluralityof twisted carbon nanotube wires, and each of the plurality of twistedcarbon nanotube wires comprise a plurality of carbon nanotubes helicallywrapped around a longitudinal axis of each of the plurality of twistedcarbon nanotube wires.
 8. The light emitting diode of claim 1, whereinthe carbon nanotube structure comprises a plurality of untwisted carbonnanotube wires, each of the plurality of untwisted carbon nanotube wirescomprise a plurality of carbon nanotubes substantially parallel to eachother and a longitudinal axis of each of the plurality of untwistedcarbon nanotube wires.
 9. The light emitting diode of claim 1, whereinthe transparent conductive layer further comprises a plurality of metalparticles dispersed in the carbon nanotube structure.
 10. The lightemitting diode of claim 1, wherein the static electrode comprises amaterial selected from the group consisting of titanium, aluminum,nickel, and gold.
 11. The light emitting diode of claim 1, wherein thestatic electrode comprises a titanium layer and a gold layer.
 12. Thelight emitting diode of claim 11, wherein a thickness of the titaniumlayer is about 15 nanometers, and a thickness of the gold layer is about100 nanometers.
 13. The light emitting diode of claim 1, wherein thestatic electrode and the second electrode have a same type and functiontogether as a P-type electrode or a N-type electrode.
 14. A lightemitting diode comprising: a substrate; a first semiconductor layerlocated on the substrate, wherein the first semiconductor layercomprises a first surface and a second surface connected to the firstsurface; an active layer located on the first surface of the firstsemiconductor layer so that the second surface is exposed; a secondsemiconductor layer located on the active layer; a first electrodelocated on the second surface of the first semiconductor layer andelectrically connected to the first semiconductor layer; a carbonnanotube layer located on and electrically connected to the secondsemiconductor layer; a second electrode located on and electricallyconnected to the carbon nanotube layer; and a static electrode locatedbetween the second semiconductor layer and the carbon nanotube layer,wherein the carbon nanotube layer comprises a first portion in directcontact with the second semiconductor layer and a second portionsandwiched between the static electrode and the second electrode, andthe static electrode is a continuous metal layer; wherein the staticelectrode and the second electrode have a same shape and area andcompletely overlap with each other.
 15. The light emitting diode ofclaim 14, wherein the static electrode and the second electrode have asame type and function together as a P-type electrode or a N-typeelectrode.
 16. A light emitting diode comprising: a first semiconductorlayer; an active layer located on the first semiconductor layer; asecond semiconductor layer located on the active layer; a firstelectrode located on and electrically connected to the firstsemiconductor layer; a carbon nanotube layer located on and electricallyconnected to the second semiconductor layer; a second electrode locatedon and electrically connected to the carbon nanotube layer; and a staticelectrode located between the second semiconductor layer and the carbonnanotube layer, wherein the carbon nanotube layer comprises a firstportion in direct contact with the second semiconductor layer and asecond portion sandwiched between the static electrode and the secondelectrode, and the static electrode is a continuous metal layer; whereinthe static electrode and the second electrode have a same shape and areaand completely overlap with each other.
 17. The light emitting diode ofclaim 16, wherein the static electrode and the second electrode have asame type and function together as a P-type electrode or a N-typeelectrode.